LeetCode —— 145. 二叉树的后序遍历【递归与迭代】（Python）

给定一个二叉树，返回它的 后序 遍历。

进阶: 递归算法很简单，你可以通过迭代算法完成吗？

解法一：递归

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = Noneclass Solution:def __init__(self):self.ans = []def postorderTraversal(self, root: TreeNode) -> List[int]:if not root:return self.ansself.postorderTraversal(root.left)self.postorderTraversal(root.right)self.ans.append(root.val)return self.ans

后序遍历算法？解法二：迭代

class Solution(object):def postorderTraversal(self, root):""":type root: TreeNode:rtype: List[int]"""if root is None:return []stack = [root, ]  # 栈，后进先出output = []  # 存储输出while stack:root = stack.pop()output.append(root.val)if root.left is not None:stack.append(root.left)if root.right is not None:stack.append(root.right)return output[::-1]  # 逆序输出